1. Field of the Invention
The present invention relates to a heat and oil resistant insulating composition used as a material for insulating layer of an electric insulating wire, an extrusion mold and a cord-shaped heater, and more particularly, to an insulating composition possible of cross-linking under the atmospheric pressure.
2. Description of the Prior Art
There are conventionally known insulating compositions excellent in heat and oil resistant property and electric characteristics, comprising an ethylene tetrafluoride-propylene copolymer, an allyl compound as a cross-linking auxiliary and an organic peroxide as a cross-linking agent.
These compositions are used as materials for an insulating layer of an electric insulating wire which is made of a conductor (stranded wire assembly) coated with the insulating layer, and the wire obtained is being utilized as a lead wire of automobiles, machine tools, motors etc., due to high heat and oil resistance, electric characteristics thereof. The composition is extruded and coated on the conductor, and then cross-linked by heating under the high pressure with pressurized vapor or liquid for preventing the occurence of the voids therein or it is extruded and coated on the conductor, and cross-linked by heating under the atmospheric pressure, after being sucked in vacuum to eliminate moisture or gas therein.
With such former process, however, the composition is intruded into spaces of the stranded wire assembly (conductor) due to the high pressure, and kept in the spaces as a rubber after the cross linking, when the coat is removed from the assembley.
Moreover, with the latter process, however, various disadvantages are encountered: it takes long time for the preparation of the production, different from the conventional extruder, the vacuum pump in the extruder must be contineously kept into a necessary vacuum degree, the vent-type extruder is high cost and requires wide places since it involves large-size cylinder and vacuum pump.
Furthermore, these compositions are used as materials for extrusion molds, such as tubes, packings, etc., which are required to hold high heat and oil resistance. The composition is cross-linked with the same steps as mentioned above.
With such conventional process, however, various disadvantages are encountered; with the former process, the production rate becomes low inspite of the increase of production steps due to the batch-type cross-linking, it requires a boiler for producing pressurized vapor, etc., and with the latter process, it contains some disadvantages as mentioned above.
Moreover, these compositions are used as materials for cord-shaped heaters which is composed of a glass fiber cord as a core, a metal resistance wire spirally wound on the core and insulating layer coated on the wire. The cord-shaped heater is being utilized in a compressor crank case of a refrigerating machine, pipeline, etc., due to excellent electric characteristics, high heat and oil resistance. The composition is cross-linked with the same steps as mentioned above.
With such conventional process, however, varions disadvantages which are same as mentioned above are encountered.